1. Field of the Invention
The present invention relates to a method and apparatus for bonding parts of a disappearing model used for casting, and particularly to a method and apparatus for bonding parts of a disappearing model in a casting method which uses a disappearing model.
2. Related Art Statement
In conventional casting methods of the type that use a disappearing model, the disappearing model is generally made of foamable synthetic resin, particularly foamable polystyrol, and is formed as one unit. However, a disappearing model having a complicated shape is formed by forming parts of the disappearing model in advance, which parts have shapes obtained by dividing the model, and then bonding them together with an adhesive to form a unit. This bonding is performed by applying an adhesive in advance on the surface of each of portions of two parts of a disappearing model to be bonded, using a brush or the like and then bringing these portions into contact with each other.
The adhesive used in this bonding process may be an ordinary adhesive such as a synthetic resin adhesive of the type in which a solvent volatilizes, or one of the type in which a hardener is mixed, or again a synthetic rubber adhesive, but a hot melt-type adhesive is the type most preferably used. Such hot melt-type adhesives are solid at room temperature but may be softened by heating to about 100.degree. C. and sufficiently melted at about 130.degree. C. to 180.degree. C. or 190.degree. C. to 210.degree. C. to assume a liquid form which can be easily applied. When such a liquid adhesive is used for bonding, the adhesive hardens immediately after bonding whereby the adhered portions become tightly bonded because the temperature thereof returns to room temperature. Various types of hot melt-type adhesive are commercially available at present. Since the compositions of these adhesives are already known, no detailed description thereof will be given here.
However, when the bonding is performed by using an adhesive as described above, an inevitable problem occurs in that the adhesive held between the portions to be adhered of the above-described two parts of a disappearing model is extruded outwardly to form a projection having a strip-like form. If the thus-formed disappearing model is used in casting, the above-described projection will be faithfully reproduced in the surface of the cast product to form a strip projecting from the surface thereof. Since the removal of such a projecting strip requires much labor and a process suitable for the purpose, extra time and expense will be involved. When such a projecting strip is formed on a portion having a complicated shape, it is in some cases difficult to apply the tool used in removing the strip and to remove it.
In order to eliminate the above-described problem, an insufficient amount of adhesive may, for example, be applied to one of the surfaces of the portions to be adhered of two disappearing model parts to be bonded so that no projection of the above-described type is produced, and the portions to be adhered together are then brought into contact with each other. In this case, portions near the margins of the surfaces to be adhered sometimes lack the adhesive and thus each have a concave cross-sectional form which results in the production of concave-shaped strips. If the thus-formed disappearing model is used in casting, such concave-shaped strips would also be reproduced faithfully in the surface of a cast product and will thus result in concave-shaped strips on the surface of the cast product. Such concave-shaped strips cause the strength of the cast product to be reduced, as well as making the appearance of the product poor, resulting in inferior products.
The present invention has been achieved with a view to solving the aforementioned problem in the production of disappearing models used for casting, and it is an object of the present invention to provide a method and apparatus for bonding parts of a disappearing model used for casting which is capable of eliminating the production of any projection formed by an adhesive and having the form of a strip on the outside of portions of the disappearing models to be adhered, as well as eliminating portions thereof which lack the adhesive and thus have a concave cross-sectional form.